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  <div class="section" id="api-and-abi-versioning">
<span id="apiabiversion"></span><h1>API and ABI Versioning<a class="headerlink" href="#api-and-abi-versioning" title="Permalink to this headline">¶</a></h1>
<p><code class="docutils literal"><span class="pre">PY_VERSION_HEX</span></code> is the Python version number encoded in a single integer.</p>
<p>For example if the <code class="docutils literal"><span class="pre">PY_VERSION_HEX</span></code> is set to <code class="docutils literal"><span class="pre">0x030401a2</span></code>, the underlying
version information can be found by treating it as a 32 bit number in
the following manner:</p>
<blockquote>
<div><table border="1" class="docutils">
<colgroup>
<col width="9%" />
<col width="31%" />
<col width="60%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Bytes</th>
<th class="head">Bits (big endian order)</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal"><span class="pre">1</span></code></td>
<td><code class="docutils literal"><span class="pre">1-8</span></code></td>
<td><code class="docutils literal"><span class="pre">PY_MAJOR_VERSION</span></code> (the <code class="docutils literal"><span class="pre">3</span></code> in
<code class="docutils literal"><span class="pre">3.4.1a2</span></code>)</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">2</span></code></td>
<td><code class="docutils literal"><span class="pre">9-16</span></code></td>
<td><code class="docutils literal"><span class="pre">PY_MINOR_VERSION</span></code> (the <code class="docutils literal"><span class="pre">4</span></code> in
<code class="docutils literal"><span class="pre">3.4.1a2</span></code>)</td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">3</span></code></td>
<td><code class="docutils literal"><span class="pre">17-24</span></code></td>
<td><code class="docutils literal"><span class="pre">PY_MICRO_VERSION</span></code> (the <code class="docutils literal"><span class="pre">1</span></code> in
<code class="docutils literal"><span class="pre">3.4.1a2</span></code>)</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">4</span></code></td>
<td><code class="docutils literal"><span class="pre">25-28</span></code></td>
<td><code class="docutils literal"><span class="pre">PY_RELEASE_LEVEL</span></code> (<code class="docutils literal"><span class="pre">0xA</span></code> for alpha,
<code class="docutils literal"><span class="pre">0xB</span></code> for beta, <code class="docutils literal"><span class="pre">0xC</span></code> for release
candidate and <code class="docutils literal"><span class="pre">0xF</span></code> for final), in this
case it is alpha.</td>
</tr>
<tr class="row-even"><td>&#160;</td>
<td><code class="docutils literal"><span class="pre">29-32</span></code></td>
<td><code class="docutils literal"><span class="pre">PY_RELEASE_SERIAL</span></code> (the <code class="docutils literal"><span class="pre">2</span></code> in
<code class="docutils literal"><span class="pre">3.4.1a2</span></code>, zero for final releases)</td>
</tr>
</tbody>
</table>
</div></blockquote>
<p>Thus <code class="docutils literal"><span class="pre">3.4.1a2</span></code> is hexversion <code class="docutils literal"><span class="pre">0x030401a2</span></code>.</p>
<p>All the given macros are defined in <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Include/patchlevel.h">Include/patchlevel.h</a>.</p>
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